What is the lead wire method of thermal resistor?

There are three types of lead wires for thermal resistors: 2-wire, 3-wire, and 4-wire.

The 2-wire thermal resistor is easy to wire, but it will bring in additional errors of lead resistance. Therefore, it is not suitable for manufacturing Class A precision thermal resistors, and the lead wires and wires should not be too long when in use.

The 3-wire system can eliminate the influence of lead resistance, and the measurement accuracy is higher than the 2-wire system. As a process detection element, it is widely used.

The 4-wire system can not only eliminate the influence of lead resistance, but also eliminate the influence of this resistance when the resistance of the connecting wires is the same. When measuring with high precision, the 4-wire system should be used.

Thermocouple temperature measurement principle

It is based on the characteristic that the resistance value of a conductor or semiconductor changes with temperature to measure temperature and temperature-related parameters. Most thermal resistors are made of pure metal materials. Currently, platinum and copper are widely used. Now, nickel, manganese, rhodium and other materials have begun to be used to manufacture thermal resistors. Thermal resistors usually need to transmit resistance signals through leads to computer control devices or other secondary instruments.

Ordinary thermal resistor

From the temperature measurement principle of thermal resistor, it can be known that the change of the measured temperature is directly measured by the change of the resistance value of the thermal resistor. Therefore, the change of the resistance of various wires such as the lead wire of the thermal resistor will affect the temperature measurement.

The armored thermal resistor is a solid body composed of a temperature sensing element (resistor), lead wire, insulating material, and stainless steel sleeve. Its outer diameter is generally φ2-φ8mm, and the smallest can reach φ0.25mm. Compared with ordinary thermal resistors, it has the following advantages: What is the lead wire method of thermal resistor?

1. Small size, no air gap inside, thermal inertia, small measurement value;

2. Good mechanical properties, vibration resistance, and impact resistance;

3. Can be bent and easy to install;

4. Long service life.

End face thermal resistor

The end face thermal resistor temperature sensing element is wound with specially treated resistance wire and is close to the end face of the thermometer. Compared with general axial thermal resistors, it can more accurately and quickly reflect the actual temperature of the measured end face, and is suitable for measuring the end face temperature of bearings and other parts.

Explosion-proof thermal resistors

Explosion-proof thermal resistors use a special structure of the junction box to confine the explosion of the explosive mixed gas inside its shell due to the influence of sparks or arcs to the junction box, so that the production site will not cause an explosion. Explosion-proof thermal resistors can be used for temperature measurement in explosion-hazardous places in Bla-B3c grade areas.

The temperature measurement principle of thermal resistors is different from that of thermocouples.

Thermal resistors measure temperature based on the thermal effect of resistors, that is, the resistance of the resistor changes with the change of temperature. Therefore, as long as the resistance change of the temperature-sensitive thermal resistor is measured, the temperature can be measured. At present, there are mainly two types: metal thermal resistors and semiconductor thermistors.

The resistance value and temperature of metal thermal resistors can generally be expressed by the following approximate relationship, namely

Rt=Rt0[1+α(t-t0)]

Wherein, Rt is the resistance value at temperature t; Rt0 is the corresponding resistance value at temperature t0 (usually t0=0℃); α is the temperature coefficient.

The relationship between the resistance value and temperature of semiconductor thermistors is

Rt=AeB/t

Wherein, Rt is the resistance value at temperature t; A and B are constants depending on the structure of the semiconductor material.

In comparison, the temperature coefficient of thermistors is larger, and the resistance value at room temperature is higher (usually more than several thousand ohms), but the interchangeability is poor, the nonlinearity is serious, and the temperature measurement range is only about -50~300℃. It is widely used in temperature detection and control of household appliances and automobiles. Metal thermal resistors are generally suitable for temperature measurement in the range of -200~500℃. They are characterized by accurate measurement, good stability, and reliable performance. They are widely used in process control.

Metal thermal resistors commonly used in industry can be seen from the change of resistance with temperature. Most metal conductors have this property, but not all of them can be used as temperature measuring thermal resistors. The metal materials used as thermal resistors generally require: as large and stable temperature coefficient as possible, large resistivity (reducing the size of the sensor at the same sensitivity), stable chemical and physical properties within the temperature range of use, good material reproducibility, and an intermediate functional relationship between the resistance value and the temperature change (preferably a linear relationship).